This paper introduces a methodology to analyze the safety of timed discrete event systems. Our case-study is
the level crossing, a critical component for the safety of railway systems. First, our goal is to take out the forbidden state
highlighted by a p-time Petri net modelling. This model deals with the requirements of the considered system and has to
contain all the constraints that have to be respected. Then we describe a process identified as a solution for the system
functioning. This method consists in exploring all the possible behaviors of the system by means of the construction of
state classes. Finally, we check if the proposed process corresponds to the model of requirements previously built.